<template>
	<view class="u-wrap">
		<view class="u-search-box">
			<view class="u-search-inner">
				<u-icon name="search" color="#909399" :size="28"></u-icon>
				<text class="u-search-text">搜索</text>
			</view>
		</view>
		<view class="u-menu-wrap">
			<scroll-view scroll-y scroll-with-animation class="u-tab-view menu-scroll-view" :scroll-top="scrollTop"
				:scroll-into-view="itemId">
				<view v-for="(item, index) in tabbar" :key="index" class="u-tab-item"
					:class="[current == index ? 'u-tab-item-active' : '']" @tap.stop="swichMenu(index)">
					<text class="u-line-1">{{ item.name }}</text>
				</view>
			</scroll-view>
			<scroll-view :scroll-top="scrollRightTop" scroll-y scroll-with-animation class="right-box"
				@scroll="rightScroll">
				<view class="page-view">
					<view class="class-item" :id="'item' + index" v-for="(item, index) in tabbar" :key="index">
						<view class="item-title">
							<text>{{ item.name }}</text>
						</view>
						<view class="item-container">
							<view class="thumb-box" v-for="(item1, index1) in item.foods" :key="index1"
								@click="clickMenu(item1)">
								<image class="item-menu-image" :src="item1.icon" mode=""></image>
								<view class="item-menu-name">{{ item1.name }}</view>
							</view>
						</view>
					</view>
				</view>
			</scroll-view>
		</view>
	</view>
</template>
<script>
import classifyData from '@/pages_template/common/classify.data.js';
export default {
	data() {
		return {
			scrollTop: 0, //tab标题的滚动条位置
			oldScrollTop: 0,
			current: 0, // 预设当前项的值
			menuHeight: 0, // 左边菜单的高度
			menuItemHeight: 0, // 左边菜单item的高度
			itemId: '', // 栏目右边scroll-view用于滚动的id
			tabbar: classifyData,

			arr: [],
			scrollRightTop: 0, // 右边栏目scroll-view的滚动条高度
			timer: null, // 定时器

		}
	},
	onReady() {
		this.getMenuItemTop()
	},
	methods: {
		// 点击左边的栏目切换
		async swichMenu(index) {
			if (this.arr.length == 0) {
				await this.getMenuItemTop();
			}
			if (index == this.current) return;
			this.scrollRightTop = this.oldScrollTop;
			this.$nextTick(() => {
				this.scrollRightTop = this.arr[index];
				this.current = index;
				this.leftMenuStatus(index);
			})
		},
		// 获取一个目标元素的高度
		getElRect(elClass, dataVal) {
			new Promise((resolve, reject) => {
				const query = uni.createSelectorQuery().in(this);
				query.select('.' + elClass).fields({
					size: true
				}, res => {
					// 如果节点尚未生成，res值为null，循环调用执行
					if (!res) {
						setTimeout(() => {
							this.getElRect(elClass);
						}, 10);
						return;
					}
					this[dataVal] = res.height;
					resolve();
				}).exec();
			})
		},
		// 观测元素相交状态
		async observer() {
			this.tabbar.map((val, index) => {
				let observer = uni.createIntersectionObserver(this);
				// 检测右边scroll-view的id为itemxx的元素与right-box的相交状态
				// 如果跟.right-box底部相交，就动态设置左边栏目的活动状态
				observer.relativeTo('.right-box', {
					top: 0
				}).observe('#item' + index, res => {
					if (res.intersectionRatio > 0) {
						let id = res.id.substring(4);
						this.leftMenuStatus(id);
					}
				})
			})
		},
		// 设置左边菜单的滚动状态
		async leftMenuStatus(index) {
			this.current = index;
			// 如果为0，意味着尚未初始化
			if (this.menuHeight == 0 || this.menuItemHeight == 0) {
				await this.getElRect('menu-scroll-view', 'menuHeight');
				await this.getElRect('u-tab-item', 'menuItemHeight');
			}
			// 将菜单活动item垂直居中
			this.scrollTop = index * this.menuItemHeight + this.menuItemHeight / 2 - this.menuHeight / 2;
		},
		// 获取右边菜单每个item到顶部的距离
		getMenuItemTop() {
			new Promise(resolve => {
				let selectorQuery = uni.createSelectorQuery();
				selectorQuery.selectAll('.class-item').boundingClientRect((rects) => {
					// 如果节点尚未生成，rects值为[](因为用selectAll，所以返回的是数组)，循环调用执行
					if (!rects.length) {
						setTimeout(() => {
							this.getMenuItemTop();
						}, 10);
						return;
					}
					rects.forEach((rect) => {
						// 这里减去rects[0].top，是因为第一项顶部可能不是贴到导航栏(比如有个搜索框的情况)
						this.arr.push(rect.top - rects[0].top);
						resolve();
					})
				}).exec()
			})
		},
		// 右边菜单滚动
		async rightScroll(e) {
			this.oldScrollTop = e.detail.scrollTop;
			if (this.arr.length == 0) {
				await this.getMenuItemTop();
			}
			if (this.timer) return;
			if (!this.menuHeight) {
				await this.getElRect('menu-scroll-view', 'menuHeight');
			}
			setTimeout(() => { // 节流
				this.timer = null;
				// scrollHeight为右边菜单垂直中点位置
				let scrollHeight = e.detail.scrollTop + this.menuHeight / 2;
				for (let i = 0; i < this.arr.length; i++) {
					let height1 = this.arr[i];
					let height2 = this.arr[i + 1];
					// 如果不存在height2，意味着数据循环已经到了最后一个，设置左边菜单为最后一项即可
					if (!height2 || scrollHeight >= height1 && scrollHeight < height2) {
						this.leftMenuStatus(i);
						return;
					}
				}
			}, 10)
		},
		clickMenu(menu) {
			console.log(menu);
		}
	}
}
</script>

<style lang="scss" scoped>
.u-wrap {
	height: calc(100vh);
	/* #ifdef H5 */
	height: calc(100vh - var(--window-top));
	/* #endif */
	display: flex;
	flex-direction: column;
}

.u-search-box {
	padding: 18rpx 30rpx;
}

.u-menu-wrap {
	flex: 1;
	display: flex;
	overflow: hidden;
}

.u-search-inner {
	background-color: rgb(234, 234, 234);
	border-radius: 100rpx;
	display: flex;
	align-items: center;
	padding: 10rpx 16rpx;
}

.u-search-text {
	font-size: 26rpx;
	color: $u-tips-color;
	margin-left: 10rpx;
}

.u-tab-view {
	width: 200rpx;
	height: 100%;
}

.u-tab-item {
	height: 110rpx;
	background: #f6f6f6;
	box-sizing: border-box;
	display: flex;
	align-items: center;
	justify-content: center;
	font-size: 26rpx;
	color: #444;
	font-weight: 400;
	line-height: 1;
}

.u-tab-item-active {
	position: relative;
	color: #000;
	font-size: 30rpx;
	font-weight: 600;
	background: #fff;
}

.u-tab-item-active::before {
	content: "";
	position: absolute;
	border-left: 4px solid $u-primary;
	height: 32rpx;
	left: 0;
	top: 39rpx;
}

.u-tab-view {
	height: 100%;
}

.right-box {
	background-color: rgb(250, 250, 250);
}

.page-view {
	padding: 16rpx;
}

.class-item {
	margin-bottom: 30rpx;
	background-color: #fff;
	padding: 16rpx;
	border-radius: 8rpx;
}

.class-item:last-child {
	min-height: 100vh;
}

.item-title {
	font-size: 26rpx;
	color: $u-main-color;
	font-weight: bold;
}

.item-menu-name {
	font-weight: normal;
	font-size: 24rpx;
	color: $u-main-color;
}

.item-container {
	display: flex;
	flex-wrap: wrap;
}

.thumb-box {
	width: 33.333333%;
	display: flex;
	align-items: center;
	justify-content: center;
	flex-direction: column;
	margin-top: 20rpx;
}

.item-menu-image {
	width: 120rpx;
	height: 120rpx;
}
</style>
